The present invention broadly relates to circuit breakers and contactors or protective relays and pertains, more specifically, to a new and improved contact arrangement for an electrical switching device, particularly for a contactor or protective relay.
Generally speaking, the contact arrangement of the present development is of the type comprising a stationary contact element and a movable contact element, whereby the stationary contact element comprises an elongated current lead-in member, a contact member mounted at an end portion of the current lead-in member, and an arc guiding or conducting element adjacently arranged at the aforesaid contact member and defining thereat a connecting or adjoining location. The arc guiding or conducting element extends in a direction substantially parallel to the current lead-in member at least in the area of the aforesaid connecting or adjoining location and is conductively connected with the current lead-in member solely or only in close proximity to the aforesaid connecting or adjoining location. The movable contact element is provided with a current-carrying connecting piece containing a contact member and situated in a manner to oppose or face the current lead-in member as well as the arc guiding or conducting element.
In European Patent Application No. 0,079,978, published June 1, 1983 there is disclosed a contact arrangement of the aforementioned type. In this known contact arrangement the stationary or fixed contact element comprises an elongated plate-shaped current lead-in member provided with a contact member mounted at an end portion thereof and an arc conducting element adjacently arranged at the aforesaid contact member and supported in electrically insulating manner at that side of the current lead-in member facing the arc chamber.
The arc conducting element is formed of ferromagnetic material and is electrically conductively connected, solely in close proximity to the contact member, by means of two rivets with the underlying current lead-in member formed of copper. At a distance from this joining location the arc conducting element is bent away to form a right angle relative to the underlying current lead-in member.
A major disadvantage of this known arrangement is seen in the fact that the arc drawn across the gap between the separating or opening contact members in a current cut-off or interrupting operation commutates in broadsurfaced manner or even only at one side to the arc conducting element leading to arc interruption plates, then further migrates or travels along the lateral edge of the arc conducting element and thereby contacts the lateral walls of the arc quench chamber consisting of insulating material. Apart from the fact that the maximum permissible cut-off current of this known contactor is confined to a relatively low range for the aforementioned reasons, the service life of the switching device turns out to be relatively short due to arcing stress of the lateral wall of the arc quench chamber.
A further known contact arrangement for a contactor comprising a stationary contact element and a movable contact element is disclosed, for example, in German Published Patent Application No. 3,302,884, published Aug. 4, 1983. The end portion of the stationary contact element provided with a contact member is bent back in U-shaped manner. A likewise U-shaped arc conducting element formed of ferromagnetic material is adjacently arranged at the contact member, the arc conducting member being bent back beneath the contact member. The arc conducting element serves to guide the switching arc between the arc interruption plates.
In order to prevent mechanical damage to the arc conducting element heated by the switching arc, there are provided protruding ribs impressed into the arc conducting element at both lateral areas thereof. The arc obviously travels along such ribs and can thus be kept away to some extent from the insulated walls of the arc quench chamber. These ribs originating or commencing relatively far away from the contact member contribute hardly anything to shortening the dwell time of the arc at the contact member and thereby to lengthen the service life of the switching device by improving commutation of the arc to the arc conducting element. This measure still provides no satisfactory increase of the maximum permissible cut-off current and practically no adequate extension of the service life of the switching device.
A further switching device containing a stationary contact element and a movable contact element is known, for example, from European Patent Application No. 0,070,413, published Jan. 26, 1983. The movable contact piece is here somewhat extended beyond the contact member and provided with an arc shield. Beside or close to the contact member of the stationary contact element and beneath the arc shield of the movable contact element in the closed contact position thereof, there is arranged an electrically conductive projection. When the movable contact member is separated from the stationary contact member, an arc commutated by the contact members is drawn between the arc shield and the projection and extinguished. Such auxiliary electrodes do not function in low-voltage switching devices, particularly in contactors with generally relatively low arc voltage, because the electric field strength at a projection is normally not sufficiently high for igniting a commutating arc.